1. Field of Invention
This invention relates to sheet feeding assemblies. In particular, this invention relates to feeding assemblies that control sheet registration and orientation.
2. Description of Related Art
Reproduction apparatuses must control sheet feeding to ensure that the original document sheet is fed in a straight, properly positioned manner to achieve accurate reproduction of the original document. Such reproduction apparatuses include copiers, scanners and facsimile machines, for example. It is also critical to feed a sheet accurately and in an aligned manner to prevent jamming of the sheet in the feed path.
There are many known sheet registration assemblies, commonly referred to as deskewing devices, that control feeding and correct misalignment. One example is U.S. Pat. No. 5,090,683 to Kamath et al. in which a sheet is initially fed to input drive rollers that convey the sheet to detectors that detect the leading edge of the sheet to signal the controller of the presence of the sheet in the assembly. Another example is U.S. Pat. No. 5,169,140 in which a sheet is initially driven with an undetected amount of skew to skew detectors and then driven differentially to deskew the sheet based on signals from the skew detectors.
An example of a sheet registration and deskewing device in use in an electrophotographic printing machine is shown in U.S. Pat. No. 5,678,159 to Williams et al and in U.S. Pat. No. 5,887,996 to Castelli. An example of use of a document deskewing system in a copier is shown in U.S. Pat. No. 4,428,667 to Phelps et al.
The above devices, however, engage and drive the sheet into the feed path before detection of the sheet. Thus, the sheet must be fed into the nip of the drive assembly prior to actuating the system, especially the deskewing system. This creates obstacles in the feed path that can create problems or require additional attention from the user. Many lightweight documents experience jamming or wrinkling when passing obstacles in the feed path. Also, the drive rolls that nip the sheet to activate the system constrict the latitude of possible sheet orientation upon input and requires greater care by the user. A system without initial obstacles that enabled easy use by all users would be desirable.
An aspect of this invention is to provide a feeding assembly that easily feeds sheets to a feed path with a high degree of accuracy.
Another aspect of this invention is to provide an assembly that has a user-friendly feel when a sheet is input to the device. Further, this invention allows a greater latitude in document input and registration during input to facilitate operation by a user.
An additional aspect to this invention is to provide an assembly that functions well with a full range of document weights.
A sheet feeding assembly according to the invention is used for feeding a sheet to a feed path. The assembly comprises a sheet input with a sheet detector that outputs a signal when a sheet is present at the input. A prefeeding mechanism is provided that is selectively engageable with the sheet at the input. A deskewing mechanism is disposed downstream of the prefeeding mechanism and controls orientation of the sheet. A controller is coupled to the sheet detector, the prefeeding mechanism and the deskewing mechanism to actuate the deskewing mechanism in response to the signal from the sheet detector and selectively engage the sheet with the prefeeding mechanism to drive the sheet to the deskewing mechanism.
The sheet feeding assembly can further comprise a limited slip clutch connected to the deskewing mechanism to cause the prefeeding mechanism to respond to the signal output from the sheet detector by moving the prefeeding mechanism toward the input. A sensor can be provided in proximity to the deskewing mechanism that detects a leading edge of the sheet to cause the prefeeding mechanism to disengage with the sheet upon a signal from the sensor.
The method of controlling a sheet feeding assembly to feed a sheet from an input to a feed path according to this invention comprises the steps of detecting the sheet at the input, actuating a driving apparatus, moving a prefeeding driving mechanism with the driving apparatus to engage the sheet, and manipulating the sheet with a deskewing apparatus to deskew the sheet with respect to the feed path.
The method can include actuating the driving apparatus with a limited slip clutch in response to detecting a sheet in the feed path to pivot the prefeeding driving mechanism toward a nip roll to engage the sheet. The method can also include automatically biasing the prefeeding driving mechanism away from the input when a sheet is not detected at the input and detecting a leading edge of the sheet within the feed path at the deskewing mechanism to disengage the prefeeding driving mechanism.
The invention also encompasses a reproduction assembly comprising an image reproduction device for reproducing images from an original document sheet. A sheet feed path extends from an input to an output past the image reproduction device. A self-actuating prefeeding device selectively engages a sheet at the input and drives the sheet into the feed path, and a controller controls engagement of the self-actuating prefeeding device based on presence of a sheet at the input of the feed path.
The reproduction assembly can further comprise a deskewing device located in the feed path downstream of the self-actuating prefeeding device for controlling orientation of the original document sheet being fed through the feed path. A sheet detector and a movable nip assembly may also be provided, wherein the deskewing device actuates the movable nip assembly to move into the feed path to engage a sheet at the input based on a signal from the sheet detector.
Other aspects, advantages and salient features of the invention will be become apparent from the following detailed description, which taken in conjunction with the drawings discloses preferred embodiments of the invention.